Is there a specific way to unlock it? I bought the five kits from the cash shop last week and I was wondering why I didn't get the extra bonus kit. Sorry if I've posted this in the wrong place. Thanks in advance for any help. :)

I'd file a ticket if you bought all 5 and didn't receive the bonus. They can look into it for you :)

you're not the only person who had this issue. apparently it has to do with using the cart vs. the purchase link, i believe? as stated above, an admin can give you the missing item.